Post-stroke shoulder pain is a major rehabilitation problem affecting up to 60% of moderate to severely impaired stroke survivors.1 Post-stroke shoulder pain is associated with poor rehabilitation outcomes, including impaired activities of daily living2 and poor quality of life (QOL).3 Surface electrical stimulation (ES) of muscles surrounding the hemiparetic shoulder is the only intervention with evidence of efficacy from multiple randomized clinical trials (RCT).4-6 Despite the evidence for therapeutic benefit, the clinical implementation of surface ES for post-stroke shoulder pain has been difficult for several reasons. First, stimulation of cutaneous pain receptors cannot be avoided. While some stroke survivors are able to tolerate one or 2-hrs of daily surface ES therapy, many are not able to tolerate the required 6-hrs. Second, in order to minimize the stimulation-induced pain, ES is delivered at a relatively high frequency between 20 and 35 Hz, which can lead to more rapid onset of muscle fatigue.7 Third, due to stimulation-induced pain and muscle fatigue, an escalating stimulation schedule is needed. Finally, clinical skill or intensive patient training is required to reliably place electrodes on a daily basis and adjust stimulation parameters to provide optimal and tolerable treatment with minimal muscle fatigue. Accordingly, Baker and Parker, the authors of the first clinical trial of surface ES for post-stroke shoulder dysfunction, concluded "Until implanted electrode systems become available... long-term use of surface electrical stimulation can be managed by only a few patients... and their families."8(p1937) In order to address the limitations of surface ES, the investigative team pioneered the development of percutaneous intramuscular (IM) ES for the treatment of post-stroke shoulder pain.9-14 Since electrodes are implanted into motor points, skilled personnel and intense patient training are not needed to ensure proper placement of electrodes for each treatment session.10, 12, 15 IM ES is less painful and better tolerated then surface ES.13, 16 Therefore, IM ES can be delivered at a lower stimulation frequency, which is associated with reduced muscle fatigue.7 The reduced pain and fatigue of IM ES obviate the need for a cumbersome escalating stimulation schedule. Accordingly, the ES and muscle contraction are reliable and there is strong patient adherence to treatment regimen.14 The investigative team completed a RCT that demonstrated the efficacy of IM ES in reducing post-stroke shoulder pain in comparison to a sling.11, 14 Post-hoc analysis further identified time from stroke onset (<18-mo) as an important predictor of treatment success.9 The initial efficacy of IM ES has been demonstrated. However, prior to acceptance by the clinical community, additional gaps in the scientific and clinical knowledge need to be addressed. 1) To date, IM ES has only been compared to a sling. It has not been compared to "usual care." 2) The investigators'RCT showed improvements in pain related QOL based on Brief Pain Inventory (BPI) question 23;however, while this measure has been validated as a component of the BPI battery, it has not been validated as a measure of QOL. 3) The mechanism of action of IM ES in reducing shoulder pain has not been rigorously evaluated. In order to begin addressing these issues, the proposed study is designed as a comparative effectiveness single-blinded exploratory RCT. The primary objective is to estimate the relative effect sizes of pain reduction associated with IM ES and "usual care." Given the added costs and risks of a minimally invasive procedure, the superiority of IM ES over "usual care" needs to be demonstrated. We will use these estimates to design and power a larger effectiveness trial. The secondary objective is to evaluate the impact of pain reduction on quality of life. Demonstration of improvement in quality of life will validate the clinical relevance of the intervention. Finally, we will explore mechanisms. The elucidation of mechanisms will further guide the refinement of the interventions. We postulate that ES reduces shoulder pain by improving glenohumeral stability. Thus we will evaluate the relative effects of these treatments on 3-dimensional stiffness characteristics of the glenohumeral joint. We further postulate that ES improves glenohumeral stability by facilitating motor recovery. Thus we will evaluate the effects of these treatments on objective measures of poststroke motor recovery.